A common problem encountered with drive elements driven by a motorized pulley and belt arrangement is that, over time, the belt drive stretches. As the maintenance of the belt tension (or tautness) is of prime importance, anything that permits the belt(s) to slacken produces a wide range of detrimental problems, such as, for example, noise, vibration, excessive belt wear and reduction in bearing life. The end result is that, eventually, the entire apparatus must be shut down for maintenance. A known solution is to arrange the motor to pivot so that as the belt drive slackens, the motor pivots away from the drive element, thereby tightening the belt(s). Thus, pivoting of the motor away from the driven element is resisted by the belt(s). However, the motor is not prevented from pivoting towards the driven element. This may result in the motor assembly bouncing due to the alternating relaxing and tightening of the belt drive acting between the pulleys. As a consequence, there is considerable risk that the motor will pivot toward the drive element during operation, thereby causing problems.